gistfile1.c

GList* new = NULL;

for (; old; old = g_list_delete_link (old, old))
  {
    if (removable)
      {
        new = g_list_prepend (new, old->data);
      }
    else
      {
        g_object_unref (old->data); /* or g_free() or whetever is appropriate */
      }
  }